The value of L/360 has been empirically determined to be a reasonable amount of deflection in horizontal structural members. This would be one inch (1") for every thirty feet (30'). Read about this history below.
Originally published June 1964
W.G. Plewes and G.K. Garden
Mechanics of Bending — Boston University
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Sunday, February 6, 2011
The curve of this arch is a segment, that is part of a circle, and the designer of the building can choose any segment of a circle that he thinks suits his design. By trial and error over many years bricklayers have worked out methods of calculating a segment of a circle related to the span of this arch, which gives a pleasant looking shape, and which at the same time is capable of supporting the weight of brickwork over the arch. The recommended segment is such that the rise of the arch is 130 mm for every metre of span of the arch.
As temporary support for brick arches it is necessary to construct a rough timber framework to the profile of the underside of the arch on which the arch bricks are laid and jointed with mortar. The timber frame is described as centering. It is fixed and supported in the opening while the bricks of the arch are being built and the coursed brickwork over the arch laid. Once the arch and brickwork above are finished the centering is removed.
A degree of both skill and labour is involved in arch building, in setting out the arch, cutting bricks for the arch and the abutment of coursed brickwork to the curved profile of the arch so that an arched opening is appreciably more expensive than a plain lintel head.
Flat Camber Arch
This is not a true arch as it is not curved and might well be more correctly named flat brick lintel with voussoirs radiating from the centre, as illustrated in Fig. 104. The bricks from which the arch is built may be either axed or gauged to the shape required so that the joints between the bricks radiated from a common centre and the widths of voussoirs measured horizontally along the top of the arch are the same. This width will be 65 mm or slightly less so that there are an odd number of voussoirs, the centre one being a key brick.
The centre from which the joints between the bricks radiate is usually determined either by making the skew or slating surface at the end of the arch 600 to the horizontal or by calculating the top of this skew line as lying 130 mm from the jamb for every metre of span. If the underside or soffit of this arch were made absolutely level it would appear to be sagging slightly at its centre. This is an optical illusion and it is corrected by forming a slight rise or camber on the soffit of the arch.
This rise is usually calculated at 6 or 10mm for every metre of span and the camber takes the form of a shallow curve. The camber is allowed for when cutting the bricks to shape. In walls built of hard coarse grained facing bricks this arch is usually built of axed bricks. In walls built of softer, fine grained facing bricks the arch is usually of gauged rubber bricks and is termed a flat gauged camber arch. This flat arch must be of such height on face that it bonds in with the brick course of the main walling. The voussoirs of this arch, particularly those at the extreme ends, are often longer overall than a normal brick and the voussoirs have to be formed with two bricks cut to shape.
Flat Gauged Camber Arch
The bricks in this arch are jointed with lime and water, and the joints are usually 1.5 mm thick. Lime is soluble in water and does not adhere strongly to bricks as does cement. In time the jointing material, that is lime, between the bricks in this arch may perish and the bricks may slip out of position. To prevent this, joggles are formed between the bricks. These joggles take the form of semi-circular grooves cut in both bed faces of each brick, as shown in Fig. 104, into which mortar is run.
TECHNICAL NOTES ON BRICK MASONRY CONSTRUCTION
January 1995, from the archives of The Brick Industry Association. Download the PDF below.
Abstract: The masonry arch is one of the oldest structural elements. Brick masonry arches have been used for hundreds of years. This Technical Notes is an introduction to brick masonry arches. Many of the different types of brick masonry arches are discussed and a glossary of arch terms is provided. Material selection, proper construction methods, detailing and arch construction recommendations are discussed to ensure proper structural support, durability and weather resistance of the brick masonry arch.
Glulam beams can replace larger cross sections of sawn timber, but will predictably be larger in cross section than their steel equivalents. The required dimensions of a glulam replacing a given dimension of sawn timber vary considerably (for the same sawn dimension) depending on the application—roof, roof with snow, or floor, as well as span. In other words, a douglas fir 4x12 can be replaced with a glulam as small as 2.5"x9" (net) for short span roof loads, while requiring one as large as 3"x13" (net) for long span floor loads.
This seems to indicate that it is possible to more accurately measure or guarantee the structural consistency of glulams compared to sawn timber, and that conversely, while structural timber not only uses the tree inefficiently during milling, it is over-engineered in many applications due to the possibility of defects. Equivalency tables for both wood and steel provided by the APA (Engineered Wood Association) can be found here or by downloading the PDF below.
The new land development code in austin, texas has been released for preview and comment.
Preview it HERE.
Imagine Austin is a comprehensive plan for the city
adopted by the City Council June 15th 2012.
*This is an edit of Chapter 1: redundancies were condensed, verbiage omitted, and structure reworked for the sake of force and clarity. All text is original to the authors of the document. The full 343 page PDF is available here.
NOTE: THE PLAN IS NOT A LEGALLY BINDING DOCUMENT: The City Charter requires that elected officials and city government use the comprehensive plan as a guide for policies and practices, including budgeting. The aspirations of the comprehensive plan, however, are far bigger and deeper than what municipal government can accomplish alone. To fully realize the community benefits it outlines, visionary individuals, groups, agencies, and plans will also need to commit to action. The whole community must sustain the work that enacts the plan, through projects small and large. (13)
ASSESSMENT: THE PRIMARY PROBLEM IS GROWTH.
Austin’s population is projected to nearly double over the next three decades. How do we accommodate more people, in a considered and sustainable fashion, while preserving what we value so that we get better not just bigger? The Imagine Austin Comprehensive Plan provides the roadmap. We must embrace the future that we want and work to make it happen.
Many of the changes Austin has seen are positive. (3)
But other changes are negative. (4)
HOW TO GROW WELL (p4, 10)
Grow as a compact, connected city: Favoring compact growth presents an alternative direction to earlier decades of sprawling, low-density development. More compact growth contains costs by capitalizing on the land and infrastructure already in place. It also enhances human connections, innovation, and urban vibrancy. Creating a more compact and efficient city is critical to our ability to connect people of all ages, backgrounds and abilities to homes, jobs, schools, arts and cultural amenities.
Expand Transportation Choices: Austin is a big city, so it’s time to build a “big-city” transportation system that serves residents with and without cars. A compact city will facilitate this while reducing maintenance costs.
Tackle the Ethnic Divide: Austinites of color are now the majority, yet we are still dealing with the legacy of segregation and racism. Poverty and people of color both are concentrated east of Interstate 35. Overall, Austinites living east of Interstate 35 are poorer, less healthy, lag academically, and share less equally in Austin’s celebrated quality of life. How can we improve their lives while also protecting longtime Eastside residents from displacement? As a city, we want to tackle this divide and close the opportunity gaps.
Integrate nature into the city: A beautiful system of outdoor places for recreation and environmental protection will define Austin as a world-class city. We need to use our creeks, their tributaries and floodplains, Lady Bird Lake, and the Colorado River to create a network of connected greenways and waterways.
Provide paths to prosperity for all: To ensure our economic strength, it is critical to a) preserve Austin’s mix of large and small businesses, b) grow our economic base, c) provide workforce training to help residents attain living-wage jobs, and d) capitalize on the city’s creative industries and cultural heritage to position the city as a national and international center for innovation and knowledge-based industries. Lastly, the music and art is not something we can afford to lose.
Develop as an Affordable, Healthy Community: We must strive to contain Austin’s cost of living. The City of Austin can more effectively incentivize affordable housing which needs to be distributed throughout the city. New mixed use areas also need to have affordably priced housing, be walkable and bikable, and be linked by transit to jobs and other centers. Healthy communities depend on easy access to walking, biking, recreation, nutritious food, quality healthcare, schools, police, &c.
Use natural resources within sustainable limits: Suburban growth is pushing Austin outward, encroaching upon and consuming natural resources. This is a problem. We have a responsibility to future generations. We must encourage independence [from fossil fuels], reduce household and commercial water use, and protect clean air and water. The City will need to enact public policies on the basis of long-term costs and consequences. We will also need to develop relationships with our Central Texas neighbors to address these issues on a regional scale.
Think creatively and work together: Austin’s spirit of creativity is powerfully manifest in the local music and arts scenes. But it also transcends Austin’s creative community and is reflected in a broad-minded, innovative approach to solving problems. Sustaining our culture of creativity and harnessing the collective energy of our people are essential to realizing the future envisioned by Imagine Austin. Lastly, as the biggest city in Central Texas, Austin has a duty to provide regional leadership on all the above issues.
STRATEGIES FOR IMPLEMENTATION (p14)
Update Land Use Regulations: Redevelopment is a primary tool to advance many of the plan’s goals. We can control this with updated land use regulations that make it easier and more profitable to develop compact, walkable places.
Pair New Regulations with Incentives: Zoning is an important tool to guide land use, but it is best used in combination with economic incentives. With grants, loans, infrastructure investments and other new tools Austin can encourage affordable housing, beautiful design, lively public places, operational improvements, more transportation options, pocket parks, low-impact development, new jobs, an expanded tax base, &c.
Look to peer cities: Austin appears on many national and even international “Best Of” lists. Austin, however, is growing much faster than many of its peers who have more established histories. We can use this to our advantage. As we seek to maintain and improve Austin’s position as a sustainable, “most livable” city, we can greatly benefit by studying and sharing best practices with peer cities around the nation and the world.
Focus on urban design: In the past, Austin development debates were often simplistically framed as developers versus neighborhoods or vs. the environment. We have a more sophisticated understanding now. Sustainability requires redeveloping the central city in “green” ways that advance multiple environmental, economic, and community goals. Well-designed new development can create community amenities and make the city more beautiful. City codes can shape projects so they fit sensitively into neighborhood contexts. By establishing high sustainability standards—for locating projects, green building practices, site design and landscaping, and multi-modal transportation corridors—Austin can harness the positive, transformative power of redevelopment.
Partner up: The City of Austin will need help to achieve its comprehensive vision. This is especially the case in its extraterritorial jurisdiction, where partnering with county governments is critical. Likewise, Austin’s strong private sector, institutions, and non-profit organizations share responsibility for shaping the future. These groups have significant resources and relationships and can do many things city government cannot.
Measure progress and adapt: As required by the City Charter, the City of Austin will review progress on the plan annually and assess the plan at least every five years. Austinites also need to engage in community-wide “how are we doing?” evaluations. The measures and reporting should be highly visible to promote accountability. If we do not see the progress we had hoped for, we will need to make adjustments — to the actions or even to the goals themselves.
*NOTE: THIS PLAN IS A LIVING, EVOLVING DOCUMENT.
WHAT IS CodeNEXT? CodeNEXT is the new City of Austin initiative to revise the Land Development Code, which determines how land can be used throughout the city – including what can be built, where it can be built, and how much can (and cannot) be built. The process is a collaboration between Austin’s residents, business community, and civic institutions to align our land use standards and regulations with what is important to the community. This initiative to revise the Land Development Code is a priority program out of Imagine Austin, our plan for the future adopted by City Council in 2012.
*A note on terminology: ZONING is part of the LAND DEVELOPMENT CODE (LDC). The Land Development Code is the set of rules and processes that guides how land is used and developed in the city of Austin. Austin’s Land Development Code regulates new development, redevelopment, zoning, subdivisions, transportation and parking, outdoor signs, site plans, drainage, watershed protection, open space, &c.
DEVELOPMENT AND IMPLEMENTATION
FOUR PRESCRIPTION PAPERS WILL SHAPE THE DISCUSSION
These Code Prescriptions represent a preview of the specific direction being taken in the new code as well as “conversation starters” to gather community feedback on whether these Prescriptions accurately reflect community values expressed in Imagine Austin. While the Code Prescription papers will not be revised based on feedback received, the feedback will be used to shape the new code.
2. HOUSEHOLD AFFORDABILITY, summary
Missing Middle Housing is a term used to describe a range of housing types fairly rare in Austin: occupying the spectrum between detached single-family housing and large multi-family housing products. Missing Middle Housing provides a range of housing types with incremental increases in density ranging from accessory dwelling units, duplexes, triplexes, fourplexes, courtyard housing, bungalow courts, townhomes, multiplexes, live/work units, studios or “micro units” as well as those offering larger units, with multiple bedrooms for family households. Missing middle housing is typically found in walkable communities, can have higher density than what we actually perceive due to their small nature, and can blend into many types of neighborhoods due to their scale and form.
By Andrew M. Busch on Southernspaces.org
Photograph by Flickr user mirsasha.
In his heavily cited article "Crossing Over: Sustainability, New Urbanism, and Gentrification in Austin Texas" Professor Busch (Miami University, Ohio, PhD UT Austin) presents a social and political history that places East Austin at the center of a series of injustices, beginning with deliberate although unofficial segregation in the 1920s, through the effects of far more benign though no less significant "new urbanism" policies felt as gentrification today.
This last point is worth emphasizing. Gentrification is complex, Dr. Busch points out, particularly because the effect (the displacement of historic communities) is not the result of malevolence or even ignorance of the value of these communities (although this is sometimes the case), but rather the consequence of structural physical and economic realities. It is hard, for example, to understate the complexity of urban density, which is both the primary vehicle of gentrifying displacement as well as arguably the only ecologically viable solution to sustain civilization on this planet. Similarly, the market incentives which drive gentrifying development, both in the case of rent gaps that developers seek to exploit as well as the significant increase in tax revenue that the municipality stands to enjoy, are impossible to ignore.
There are times, to me, when it seems that gentrification seems but one more instance in which the dispossessed and disadvantaged are fated to suffer further injustice. But I also want to believe that the political apparatus is not so callous; I want to believe that there is value to every station in life and that the difficulty turns primarily on representing this value. How do we put it in economic terms? How can we insert the value of preserving historical continuity of minority populations and socio-economic diversity in urban cores into the equation? Since market capital and wealth generation drive the American machine, it will, unfortunately, not suffice simply to leverage an aesthetic or moral argument no matter how much we wish it to be the case.
This is not impossible. I am not an economist and only an amateur urban theorist, but I am willing to venture that intrinsically, any society which assumes a hierarchy of wealth distribution (as opposed to a communist scheme) will function most efficiently when certain needs are met (including and specifically socio-psychological needs satisfied by a sense of community) in all quartiles of the distribution—and moreover, that the system functions most efficiently when a spatial mixture of demographics is maintained to provide services and security. Jane Jacobs discusses this in her work.
What remains clear is the issue will be the exigent crisis facing our generation of young architects. Whether we can resolve the simple fact that dense urban living, ecologically and culturally imperative, is inherently expensive will determine much of the fate of the planet, I fear. Will we find economic solutions where incentives are not perversely aligned? Or must we rely on benevolent policy to subsidize the market in support of moral positions that are continuously threatened by the bottom line?
Here you will find a collection of the work that influences my thinking. It is largely a place for me to organize my notes, but I intend for it to serve as a searchable compendium that may be useful to others.